基于叠层结构的本体异质结有机太阳电池

研究了叠层结构的本体异质结有机太阳电池,下层电池由共轭聚合物（MEH-PPV）作为光敏层,上层电池由共轭聚合物（1VIEDPPV）和ZnO纳米颗粒（50nm）组成光敏层。器件结构为ITO／PEDOT：PSS／MEHPPV／Ag／MEH-PPV：ZnO／Al。与单层有机太阳电池（ITO／PEDOT：PSS／MEH-PPV／Al）相比,叠层结构的开路电压Voc是单层电池的3．7倍,短路电流Jsc是单层电池的1．6倍。     

Conjugated dendritic oligothiophenes for solution-processed bulk heterojunction solar cells

This mini-review summarizes the recent achievements of developing conjugated dendritic oligothiophenes (DOT) for use in solution-processed bulk heterojunction (BHJ) solar cells. These DOTs are structurally defined molecules with relatively high molecular weight. Therefore, this novel class of thiophene based material possesses not only some advantages of oligomers,such as defined and monodispersed molecular structure,high chemical purity, but also some characteristics of polymers, for example, good solution-processability.In addition, the step-by-step approach of its synthesis allows precise fimctionalization of dendritic backbones with desired moieties, which is helpful to finely tune the optical and electronic properties of materials. Power conversion efficiencies (PCE) of BHJ solar cells were achieved up to 2.5% when functionalized thiophene dendrimers were used as electron donor and electron acceptor was a fullerene derivative. These results indicated that dendritic oligothiophenes are a novel class of the materials of electron donor for solution-processed organic solar cells.     

Study of organic solar cells with stacked bulk heterojunction structure

Organic solar cells with stacked bulk heterojunction(BHJ) are investigated based on conjugated polymer.By using the solution spin-coating method,Poly [2-methoxy,5-(2' -ethyl-hexyloxy) -1,4-phenylene vinylene](MEH-PPV) and ZnO nanoparticles(50 nm) are mixed as the optical sense layer.Ag is used as inter-layer to connect the upper BHJ cell and the lower cell.The structures are ITO/PEDOT:PSS/MEH-PPV /Ag / MEH-PPV:ZnO /Al.The open circuit voltage(VOC) of a stacked cell is about 3.7 times of that of an individual organic solar cell(ITO/PEDOT:PSS/MEH-PPV /Al).The short circuit current(JSC) of a stacked cell is increased by about 1.6 times of that of individual one.     

正置倒置异质结有机小分子太阳能电池

以MoO3为阳极修饰层,以Rubrene/C60为活性层,制备了正置和倒置异质结有机小分子太阳能电池。实验结果表明倒置器件的开路电压Voc、短路电流密度Jsc、填充因子FF和功率转换效率η比正置结构的器件分别提高了34%、20%、25%和102%。当插入BCP阴极缓冲层后,阻挡了热的Al原子对C60层的破坏,对倒置器件的性能没有明显的影响,但却显著改善了正置器件的性能,并分析了MoO3和BCP对倒置和正置器件的作用。     

有机体异质结太阳能电池的数值模拟

引入了一种可以直观展现出聚合物体异质结太阳能电池的伏安特性的数值模型,该模型是由双分子复合以及温度和电场效应下自由载流子产生的机制。这个在聚合物材料中的到很好的体现,该材料中空间电荷效应只起到微弱的作用,从而在模型中形成相对恒定的电场。此外,在短路条件下只有7%的自由载流子由于双分子复合而消失。该模型证明在PPV/PCBM太阳能电池中随着空穴迁移率的增加和减少受体0.5电子伏特将得到5.5%最高转换效率。     

有机太阳能电池结构研究进展

有机太阳能电池因具有成本低、质轻、柔韧性好、可大面积印刷制备的优点而受到广泛关注,对电池结构进行优化可以改善有机太阳能电池的性能。综述了有机太阳能电池结构优化的最近研究进展,包括单层Schottky电池、双层异质结电池、本体混合异质结电池、叠层电池和p-i-n电池,讨论了有机太阳能电池的发展趋势和应用前景。     

利用Rubrene/C70异质结提高有机太阳能电池的性能

用C70、C60作为受体,Rubrene、CuPc作为给体,制备了4种异质结有机太阳能电池（（）SCs）。实验结果表明,c70代替Qo作为受体的OSCs短路电流Jsc显著增加;Rubrene代替CuPc作为给体的OSCs的开路电压Voc大幅度提高。制备的Rubrene／G70异质结OSCs的Voc、Jsc填充因子FF和...     

Magnetoconductance of polymer–fullerene bulk heterojunction solar cells

The organic magnetoconductance (MC) effects in poly(3-hexylthiophene): [6,6]-phenyl-C61-butyricacid methylester based bulk heterojunction solar cells were studied in dark and under illumination. The correlations between the MC and current character were revealed in this study. Results show that the dark current always exhibits a negative MC whereas a sign change in MC under illumination occurs at the bias around the open circuit voltage V_oc. We suggest that the positive MC in photocurrent is due to the field dependent conversion of singlet electron–hole pairs to triplet states and the negative MC is associated with space charge limited current with traps. Other possible mechanisms about the magnetoconductance effects are also discussed.     

New soluble porphyrin bearing a pyridinylethynyl group as donor for bulk heterojunction solar cells

Bulk heterojunction solar cells were fabricated using the blend films of a porphyrin bearing pyridinylethynyl group (POR) as electron donor and PC₆₀BM or PC₇₀BM as electron acceptor. Photoluminescence measurement of the blend films of POR with fullerene derivatives indicated that charge transfer was possible between POR and fullerene derivatives. The solution processed bulk heterojunction solar cells using the blend of POR with PC₆₀BM and PC₇₀BM exhibit overall power conversion efficiency (PCE) of 1.96% and 2.54%, respectively. The PCE of the BHJ solar cell has been further improved up to 3.27% when thermally annealed POR:PC₇₀BM was used as active layer, which is attributed mainly to the increase in short circuit current. The increase in J_sc is attributed to the enhanced crystallinity of the blend (particularly POR) and efficient π-electron conjugation of POR, resulting to an improvement in hole mobility, leading to more balance charge transport. The PCE of the device based on as cast POR:PC₇₀BM has been further improved up to 4.06% when DMF treated PEDOT:PSS buffer layer was used.     

High-resistivity sol-gel ITO thin film as an interfacial buffer layer for bulk heterojunction organic solar cells

Bulk heterojunction organic solar cells have been fabricated by inserting a high-resistivity sol-gel ITO buffer layer between an ITO anode and a PEDOT:PSS hole injection layer. The performance of the devices with the sol-gel ITO atop the ITO anodes treated by conventional annealing at 500 °C for 1 h and rapid thermal process (RTP) at 800 °C for 20 and 30 s was compared. The best power conversion efficiency of 3.5% was achieved for the device with the 15-nm-thick sol-gel ITO treated with RTP at 800 °C for 30 s, as compared with 2.7% of the standard device under an illumination of AM 1.5. In addition, the short circuit current of the device was significantly increased by 42.7%. The observed enhancement of the short circuit current can be attributed an interfacial energy step created by the high-resistivity sol-gel ITO between the ITO anode and the PEDOT:PSS.     

Tail states recombination limit of the open circuit voltage in bulk heterojunction organic solar cells

An analytical theory is presented for bimolecular recombination through tail states and open circuit voltage in bulk heterojunction organic solar cells. It is developed rigorously using the hopping transport and the drift diffusion theory. Based on the proposed model, a variety of temperature, energy disorders of the material and illumination intensity dependencies of the open circuit voltage can be well described. Good agreement between the calculation and recent experimental data is found.     

High open circuit voltage in efficient thiophene-based small molecule solution processed organic solar cells

We have synthesized and fully characterized an oligothiophene small organic molecule for its use as electron donor moiety in solution processed bulk-heterojunction organic solar cells. Our results show that device solvent annealing process of the conjugated oligothiophene molecule leads to a light-to-energy conversion efficiency of 3.75% under standard illumination conditions. The solar cell presents open-circuit voltage and fill factors as high as 1.01 V and 63.05% respectively, which are among the highest values obtained for small molecule solution processed organic solar cells.     

Recent progress and future aspects of organic solar cells

This article aims to review the recent progress and future aspects of organic solar cells (OSCs). Different device designs proposed for efficient light harvesting and their advancements have been discussed. We have discussed various parameters limiting their efficiency and their possible solutions. Special attention has been paid to understand the device physics and its fundamental facets. Open circuit voltage (V_oc) is an important parameter in the determination of their efficiency, but the picture behind the real origin of V_oc is not very much clear; therefore, this issue has been discussed in detail. Short lifetime is another important issue; therefore, recent progress in stability and related issues has also been discussed. The progress in roll to roll (R2R) processing and demonstration for large‐area OSCs has been paid particular attention. The areas, where further advances will help in the commercial realization of this technology, have also been discussed. Copyright © 2011 John Wiley & Sons, Ltd.     

Efficient electron-blocking layer-free planar heterojunction perovskite solar cells with a high open-circuit voltage

Perovskite solar cells (PSCs) with a simple device structure are particularly attractive due to their low cost and convenient fabrication process. Herein, highly efficient, electron-blocking layer (EBL)-free planar heterojunction (PHJ) PSCs with a structure of ITO/CH₃NH₃PbI₃/PCBM/Al were fabricated via low-temperature, solution-processed method. The power conversion efficiency (PCE) of over 11% was achieved in EBL-free PHJ-PSCs, which is closed to the value of PSC devices with the PEDOT:PSS as the EBL. It is impressed that the open-circuit voltage (V_oc) up to 1.06 V, an average value of 1.0 V for 43 devices, was obtained in EBL-free PHJ-PSCs. The electrochemical impedance spectroscopy (EIS) results suggested that the high PCE and V_oc are attributed to the relatively large recombination resistance and low contact resistance in EBL-free PHJ-PSCs. The solution-processed, EBL-free PHJ structure paves a boulevard for fabricating high-efficiency and low-cost PSCs.     

Realization of solution processed multi-layer bulk heterojunction organic solar cells by electro-spray deposition

Electro-spray deposition (ESD) was applied to fabricate solution processed donor–acceptor bulk heterojunction organic photovoltaic devices with multi-layer structure. Solvent effect was observed when using different organic solvents. Power conversion efficiency (PCE) of the devices prepared from dichlorobenzene increased dramatically comparing to the ones from chloroform, owing to improved homogeneity of the films. ESD enabled us to fabricate solution processed multi-layer (donor/donor:acceptor/acceptor) devices with simple successive deposition steps. Energy Dispersive X-ray Reflectometry analysis confirmed distinct three layered structure of the active layers. Solar cell device parameters of the trilayer devices were compared to single layer devices and those of spin coated devices with the same donor:acceptor ratio and film thickness. Post-thermal treatment results showed that after annealing at 125 °C, trilayer devices exhibited best performance with the maximum PCE of 2.17%.     

Determination of the optical constants of bulk heterojunction active layers from standard solar cell measurements

The determination of the optical constants n(λ) and k(λ) for organic bulk heterojunction (BHJ) active layers from standard solar cell measurements is presented. We show for a small molecule based as well as for polymer solar cells that the complex refractive index can be derived from the external quantum efficiency (EQE) in combination with current–voltage curves obtained from a series of devices with different active layer thicknesses. The results are compared to those obtained via established techniques and the impact of differences in n(λ) and k(λ) on the solar cells is shown by simulation of the current density using a transfer matrix model.     

Short‐circuit current of solar cells under artificial light

A model to estimate the short‐circuit current of a solar cell under artificial light from the short‐circuit current of the same solar cell under AM1.5 1 kW/m² is described. The results may help designers of solar‐powered portable equipment and consumer products working indoors or under a mixture of artificial and sunlight. It is concluded that the ratio of the short‐circuit currents of the same solar cell generated under fluorescent light of 1 lux illuminance divided by the short‐circuit current generated under standard 1 Sun AM1.5 conditions is around 3 × 10⁻⁶ for typical crystalline silicon and CIS solar cells. This value is one order of magnitude greater if the light source considered is an incandescent lamp. In the case of amorphous silicon solar cells the value of the ratio is close to 8 × 10⁻⁶ either for fluorescent or incandescent lamps. CdTe solar cells are also considered, and this factor is about 4 × 10⁻⁶ under fluorescent light, and four times bigger when an incandescent lamp is used. Some measurements performed validate the figures obtained. Copyright © 2002 John Wiley & Sons, Ltd.     

Controlling the morphology of nanofiber-P3HT:PCBM blends for organic bulk heterojunction solar cells

Within the field of organic bulk heterojunction solar cells, the morphology of the active layer has a key role in obtaining high power conversion efficiencies. P3HT nanofibers, obtained in highly concentrated solutions, are able to give controlled morphologies directly upon deposition. Since the solar cell efficiency of fiber solar cells depends on the fiber content of the casting solution, it is important to control this parameter. Here, we demonstrate an easy way to control the fiber content in the casting solution, i.e. changing the solution temperature. By using solution heating, the overall molecular weight of the polymer in the blend is kept constant, fiber isolation is not needed and the use of solvent mixtures is avoided. The obtained optimal power conversion efficiency is shown to be linked to the morphology of the active layer, which is studied with Transmission Electron Microscopy (TEM).     

Carbazole-based small molecules for vacuum-deposited organic photovoltaic devices with open-circuit voltage exceeding 1 V

Fabrication of vacuum deposited small molecules organic solar cell with open-circuit voltage (V_oc) exceeding 1 V is crucial in advancing the applications of organic photovoltaics (OPVs). Here, a novel carbazole-based donor-π bridge-acceptor (D-π-A) of p-type material (F-series) in combination with fullerene derivative C₆₀ or C₇₀ as n-type material for bulk-heterojunction OPVs with the structure of ITO/MoO₃ (15 nm)/F-series donor: C₆₀ or C₇₀ (40 or 80 nm)/BCP (7 nm)/Ag (120 nm) have been proposed. The vacuum deposited small molecules OPV with the donor layer consisting of F1 combined with the electron acceptor C70 exhibits a high power conversion efficiency (PCE) of 4.93%. The higher PCE of the OPV is attributed to the large V_oc value of 1.02 V. The analysis of photophysical properties using a time-dependent density functional theory model and the B3LYP functional corroborates the experimental results and provides the evidence on increasing the V_oc of OPVs.     

Influence of molar mass ratio,annealing temperature and cathode buffer layer on power conversion efficiency of P3HT:PC71BM based organic bulk heterojunction solar cell

In bulk heterojunction (BHJ) solar cells, the molar mass ratio of donor-acceptor polymers, the annealing temperature (T_an) and the cathode buffer layer plays very consequential role in improving the power conversion efficiency (PCE) by tuning the film morphology and enhancing the charge carrier dynamics. A comprehensive understanding of each of these factors is essential in order to optimize the performance of organic solar cells (OSCs). Albeit there are several fundamental reports regarding these factors, an altogether meticulous correlation of these physical processes with experimental evidence of the photo active layer are required. In this work, we systematically analyzed the influence of different molar mass ratio, the annealing temperature (T_an) and the cathode buffer layer of rrP3HT:PC₇₁BM based BHJ solar cells and their corresponding photovoltaic performances were correlated carefully with their thin film growth structure and energy level diagram. The device having 1:0.8 molar mass ratio of rrP3HT:PC₇₁BM and T_an = 150 °C annealing temperature with Bathocuproine (BCP) as the cathode buffer layer having ITO/PEDOT:PSS/rrP3HT:PC₇₁BM (molar mass ratio = 1:0.8; (T_an = 150 °C)/BCP/Al) configuration showed the best device performance with PCE, ɳ = 4.79%, Jsc = 14.21 mA/cm², V_oc = 0.58 V and FF = 57.8%. This drastic variation in PCE of the device having BCP/Al as the cathode contact compared to the other device configurations is due to the coalesced effects of better hole-blocking capacity of BCP along with Al and better phase separation of the active blend layer at 150 °C annealing temperature. These results explicate the cumulate role of all these physical parameters and their combined contribution to the PCE amendment and overall device performance with rrP3HT:PC₇₁BM based organic BHJ solar cell.